Last reviewed by the Haute Lawyer editorial team · August 2026 · Profile information is reviewed for accuracy. Learn about our editorial standards →
Mark J. O'Brien
Criminal Defense Lawyer
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Biography
Mark J. O'Brien, Esquire, is the founder and managing partner of O'Brien Hatfield, PA, a criminal defense law firm based in Tampa, Florida, that focuses on nationwide federal criminal defense and statewide criminal defense and criminal appeals.
Mark has practiced criminal law exclusively since 1998. He began his career as a prosecutor in the Miami-Dade County State Attorney's Office, rising through the ranks before transitioning to defense work. As a former Federal and State Prosecutor, Mark brings invaluable insider knowledge of how the government builds and prosecutes criminal cases.
Mark handles federal criminal cases in federal courts statewide and throughout the United States. He is widely lauded by federal judges and federal prosecutors as one of the best federal defense attorneys in Florida. His practice encompasses white collar criminal defense, federal investigations, healthcare fraud defense, drug trafficking defense, and complex criminal matters at both the state and federal level.
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Profile last reviewed: August 3, 2026
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Location
Mark J. O'Brien, P.A.
511 West Bay Street, Suite 330
Tampa, Florida 33606
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Frequently Asked Questions
What is Mark J. O'Brien's primary practice focus?
Mark J. O'Brien specializes in federal criminal defense, representing individuals and corporations charged with crimes in federal courts nationwide. His practice includes white-collar offenses (fraud, tax crimes, insider trading, money laundering), drug trafficking, firearms crimes, sex offenses, and criminal appeals at both federal and state levels.
Where is Mark J. O'Brien licensed to practice?
O'Brien holds active bar licenses in Florida (1998), Massachusetts (1998), and Montana (2023). He is also admitted to the U.S. Supreme Court and maintains pro hac vice or direct admissions to federal appellate courts (1st, 2nd, 9th, and 11th Circuits) and federal district courts in over 30 jurisdictions across the United States.
What is Mark J. O'Brien's professional background before criminal defense?
O'Brien began his legal career as a prosecutor in the Miami-Dade County State Attorney's Office in the late 1990s, where he tried over 30 cases to verdict and handled thousands of criminal matters. He rose to the level of felony prosecutor before founding O'Brien Hatfield PA in 2002 to apply his prosecution experience to criminal defense strategy.
What awards and recognitions has Mark J. O'Brien received?
O'Brien has been selected to Super Lawyers (2016–2024), maintains a 10.0 rating on Avvo (Superb), has received the Avvo Clients' Choice Award, and been recognized by Haute Lawyer and other legal directories. Federal judges have commended his advocacy and courtroom skill in published opinions.
This information is provided for general reference only and does not constitute legal advice or create an attorney–client relationship.
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